An A/D conversion technique regarded as a so-called single-slope integration type or ramp signal comparison type has been known in the past, in which A/D conversion technique, an analog unit signal and a ramp-shaped reference signal for conversion to digital data is compared with each other and, in parallel to this comparison processing, counting processing is carried out such that digital data of the unit signal is acquired on the basis of a count value at a time point when the comparison processing is completed (for example, refer to Patent Document 1).